Modern packet-oriented communications networks—also referred to as “data networks”—have been designed essentially for the transmission of packet streams, which are also referred to in the specialist world as “data packet streams”. There is normally no requirement for a guaranteed transmission quality of service. The data packet streams are thus transmitted, for example, with fluctuating time delays, since the individual data packets of the data packet streams are normally transmitted in the sequence of their access to the network, e.g. the time delays become greater the greater the number of packets that have to be transmitted by a data network. In the specialist world, the transmission of data is therefore also referred to as a transmission service without realtime conditions, or as a “non-realtime service”.
In the course of the convergence of line-oriented speech and packet-oriented data networks, realtime services, e.g. transmission services in realtime conditions, such as the transmission of speech information or moving picture information, are likewise increasingly being provided in packet-oriented communications networks. That is, the transmission of the realtime services which, until now have normally been transmitted on a line-oriented basis is being carried out on a packet-oriented basis, e.g. in packet streams, in a convergent speech/data network. These packet streams are also referred to as “realtime packet streams”. One problem that arises in this case is that a high quality of service is required for packet-oriented transmission whose quality is comparable to that of line-oriented transmission. In particular, a minimal delay—for example of <200 ms—without any fluctuations in the delay time is important, since realtime services in general require a continuous information flow, and any loss of information, for example due to packet losses, cannot be compensated for by repeated transmission of the packets that have been lost. Since, in principle, these quality of service requirements apply to all communications networks using packet-oriented transmission, they are independent of the specific configuration of a packet-oriented communications network. Consequently, the packets may be in the form of Internet, X.25 or frame-relay packets, or else may be in the form of ATM cells. Packet data streams and realtime packet data streams are in this case exemplary embodiments of traffic streams that are transmitted in communications networks.
Speech and picture information should normally be transmitted in a speech/data network with a guaranteed quality of service, in order that the quality of the speech and picture transmission is not decreased when the number of packets to be transmitted in the Internet rises. In the IETF (Internet Engineering Task Force), proposals relating to this have been made in Blake et. al., “An Architecture for Differentiated Services”, RFC 2475, 1998, ftp://venera.isi.edu/in-notes/rfc2475.txt and in Nichols et. al, “Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers”, RFC 2474, 1998, ftp://venera.isi.edu/in-notes/rfc2474.txt, for a number of service classes to be introduced in the packet-oriented Internet, which until now has not guaranteed qualities of service. An Internet such as this is also referred to as a ‘DiffServ network’. In this case, the individual packet streams are in each case allocated to a specific service class and, depending on their service class, are transmitted with or without priority with respect to packets in other service classes by the transmission nodes in the Internet. It is thus possible, by way of example, to ensure the quality of service required for realtime services by allocating the associated realtime packet streams to a service class which is transmitted with priority by the nodes in the Internet—with the realtime packet streams thus being given priority over the data packet streams.
The formation of a class for prioritized transmission results in the formation of a (virtual) separate communications network within the Internet, for transmission of high-priority traffic streams and with a separate overall transmission capacity, which comprises a portion of the overall transmission capacity of the Internet. The overall transmission capacity of a communications network which comprises transmission nodes and paths is regarded as that capacity which is required for transmission of the traffic streams which can be transmitted without any loss of traffic. That is, no further traffic stream could be transmitted in that communications network without loss of traffic. The transmission capacity which is still available on a predetermined route between two transmission nodes in the communications network accordingly depends not only on the traffic which is being transmitted directly between these two transmission nodes, but also on that traffic which is being transmitted at least partially along the given route as a consequence of transmission along other routes in the communications network.
In principle, network access control is required, at least for the prioritized traffic, for priority-controlled transmission, since the required quality of service can be ensured only if the communications network is not supplied with any more prioritized packets than the maximum number which it can transmit. For this purpose, network access devices—also referred to as ‘edge devices’ or else, from the point of view of the communications network, as ‘access nodes’—have been proposed for the Internet with a number of service classes, and which are used to provide network access control. In this case, the edge devices can                control the volume of the traffic supplied in the form of packet streams to the communications network;        set priority tags in the packets in accordance with the priority of their packet streams;        control and if necessary correct priority tags for packet streams, if the packets have already been tagged with priorities; and        control the transmission capacity of prioritized packet streams.        
The transmission nodes, which are known as edge devices, and paths in the communications network are also referred to as “domains”, with which the edge device is associated. One edge device may also be associated with a number of domains.
A fixed threshold value, which the traffic volume should not exceed, is normally set in the edge devices in order to control the traffic which is supplied to the communications network. This method is very simple, but is inflexible with regard to changes in the overall transmission capacity of the communications network.